High-Resolution Photoelectron Spectroscopy of NO <sub>3</sub> <sup>–</sup> Vibrationally Excited Along Its ν <sub>3</sub> Mode
Jascha A. Lau, Martin DeWitt, Peter R. Franke, John F. Stanton, Daniel M. Neumark
Abstract
The nitrate (NO 3 ) radical has long been the subject of both experimental and theoretical studies due to its complex electronic structure resulting from vibronic interactions between its X̃ 2 A 2 ′ and B̃ 2 E ′ states. In particular, the definite assignment of the fundamental of its degenerate stretching vibration (ν 3 ) is still under debate. Here, we report high-resolution photoelectron spectra of vibrationally pre-excited NO 3 – using the recently developed IR-cryo-SEVI technique. The anions are excited through infrared (IR) excitation near 1350 cm –1, accessing the ν 3 and 2ν 3 ( e ′) vibrational levels with band centers at 1350.5 and ∼2700 cm –1, respectively. The IR-cryo-SEVI spectrum for 2ν 3 pre-excitation shows clear evidence for an intense 3 2 1 transition. From the position of this feature (30031 cm –1 ), the electron affinity of NO 3 also determined in this work (31680 cm –1 ), and the IR excitation energy, we obtain a fundamental frequency of 1051 cm –1 for the ν 3 fundamental of the NO 3 radical. This assignment and other features in the IR-cryo-SEVI spectra are supported by spectral simulations based on a vibronic Köppel–Domcke–Cederbaum Hamiltonian. The simulations also show that nearly all features in the IR-cryo-SEVI spectra arise because of pseudo-Jahn–Teller coupling between the X̃ and B̃ states of NO 3 . The results and analysis presented here settle a long-standing controversy regarding the ν 3 frequency of NO 3 .